Put simply, the polls show that Boxer is weak, with more voters having a negative than positive opinion of her. This impression will be hard to change, so Boxer’s campaign has little choice but to go after Fiorina hard — both by defining her as out of the California mainstream on policy (look for Fiorina’s most conservative statements about abortion, climate change and guns to be recycled) and also personally.

The question for Boxer is: can she do this effectively? After three terms in the U.S. Senate, she finds herself in a box. Boxer always has sounded like an insurgent, railing at the power structure, but now she’s an entrenched incumbent and part of that structure.

She also may find Fiorina a trickier target than the three men she’s defeated in her previous Senate elections. Fiorina may have been a controversial executive with a mixed record at Hewlett Packard, but the advantage of having had a tough CEO gig is that she’s used to being under fire. Fiorina is no Meg Whitman, but she is almost certain to have a better-funded campaign than Boxer’s previous opponents. There's another reality: Boxer's attempts to portray Fiorina as a cold-blooded, job-cutting CEO (a portrait that matches Fiorina's self-portrait in her own autobiography) may be complicated by another side of Fiorina -- as a warm-blooded, persevering cancer survivor.

Boxer also may have difficulty getting people to pay attention to her attacks on Fiorina. The governor’s race is sucking up a lot of oxygen and TV time, so simply getting on the air with a message that distinguishes itself from all the other political noise will be difficult and expensive.

Boxer, as a liberal Democrat who is to the left of her center-left state on many issues, has lived a charmed political life, with California Republicans putting up a series of weak candidates against her. Boxer still leads in the polls, albeit narrowly, and it will be tough to oust her. But this may be the year her luck will run out.